Relationship of urinary sodium/potassium excretion and calcium intake to blood pressure and prevalence of hypertension among older Chinese vegetarians.

OBJECTIVE

To examine the associations of dietary sodium and potassium, as reflected by the urinary sodium/potassium excretion, and calcium intake with blood pressure and the prevalence of hypertension among older Chinese vegetarians in Hong Kong.

DESIGN

Cross-sectional study.

SETTING

Research clinic in a teaching hospital in Hong Kong.

SUBJECTS

A total of 111 ambulatory vegetarians over the age of 55 were recruited from members of religious organizations or old age hostels.

MAIN OUTCOME MEASURES

Hypertension was defined as supine blood pressure >140/90 mmHg or a history of hypertension. Dietary sodium, potassium and calcium intakes were assessed by 24 h recall method or fasting urinary sodium or potassium/creatinine ratios.

RESULTS

Seventy-one subjects (64%) were found to have hypertension. Compared with normotensive subjects, hypertensive subjects had lower calcium intake (411+/-s.d. 324 vs 589+/-428 mg, P=0.04), but higher urinary sodium/creatinine ratio (32.6+/-19.3 vs 21.0+/-12.4, P=0.00) and sodium/potassium ratio (4.7+/-2.8 vs 3.4+/-2.3, P=0.02). Among 88 subjects not taking diuretics or antihypertensive drugs, systolic blood pressure was related to calcium intake (r=-0.40), urinary sodium/creatinine ratio (r=0.39), urinary sodium/potassium ratio (r=0.30) and age (r=0.23). Diastolic blood pressure was related to urinary sodium/creatinine (r=0.29). Twenty-three subjects with high urinary sodium/potassium and low calcium intake and 16 subjects with low urinary sodium/potassium ratio and high calcium intake differed markedly with respect to systolic blood pressure (159+/-26 vs 130+/-15 mmHg) and prevalence of hypertension (78% vs 25%).

CONCLUSIONS

Older Chinese vegetarians are predisposed to hypertension because of their sodium-rich but calcium-deficient diets.